Preliminary Assessment Of Climate Change In The Lancang River Basin Based On CMIP6 Data Set

Based on the improved rank scoring method,24 GCMs' experimental historical data of precipiation and temperature were used to evaluate the model simulation effects of precipitation and air temperature in each region of the Lancang River basin,then,the future climate change in each region was estimated.Before the assessment,the spatial and temporal distribution characteristics of precipitation and temperature in the past 61 years were analyzed.The main conclusions reached are as follows:(1)The spatial distribution of precipitation and air temperature in the watershed is uneven,decreasing from south to north,and the precipitation in the central and southern regions showed a decreasing trend,while the northern region had the opposite trend.The annual and seasonal precipitation varies greatly in each region,and maintains a consistent change trend in the past over a certain period.The temperature has an increasing trend and has a strong continuity.The winter temperature increase rate is the largest.The temperature was mostly low temperature anomalies before 1997,and then high temperature anomalies.(2)Most of the models could simulate the trends of precipitation and temperature consistent with the corresponding areas,but the simulation of temperature was underestimated,and the simulation of precipitation was overestimated,especially the precipitation simulation value in the upper part of the basin was high.For temperature simulation,most of the models had good spatial correlation and relatively poor time correlation.For precipitation simulation,most of the models had bad spatial correlation and time correlation.The better overall simulation model has a stronger ability to simulate individual meteorological elements.However,the geographical environment of the Lancang River varies greatly,and the simulation effects of each model also differ greatly.The optimal models for comprehensive evaluation in the south,middle,and north are: IPSL-CM6A-LR,Can ESM5,and Nor ESM2-MM.(3)From 2015 to 2100,the temperature and precipitation in three scenarios of the three different areas of the Lancang River basin showed a significant increase trend.Among them,the temperature increase rate under the SSP5-8.5 scenario is the largest,which can reach three times the previous temperature increase rate.The precipitation increase trend is the largest in the southern part of the basin and the smallest in the north.There is some uncertainty in the prediction of future precipitation in the central basin.Under the three scenarios of SSP2-4.5,SSP3-7.0 and SSP5-8.5,the highest temperature increase rate in the southern part of the basin is in spring,while the highest temperature increase rate in the central and northern parts of the basin is in winter.The highest precipitation increase rate is basically in summer,but under the SSP5-8.5 scenario the increase rate of precipitation in the southern and central parts of the basin is much higher than that in the northern part of the basin,which can be more than 2.5 times.